#include <stdio.h>

int main(){
    int n,key; //n=5
    scanf("%d",&n);
    int arr[n];
    for(int i=0;i<n;i++)
        scanf("%d",&arr[i]);
        scanf("%d",&key);
        int low=0,high=n-1,found=0;
        while(low<=high){
            int mid=(low+high)/2;
            if(arr[mid]==key){
                printf("Element found at index %d\n",mid);
                found=1;
                break;
        }
        else if(arr[mid]<key){
            low=mid+1;  //search right half
        }
        else{
            high=mid-1; //serach left half
        }
    if(!found)
        printf("Element not found\n");
    
  return 0;
}